Conventionally, a display device which displays a video image of an omnidirectional camera on a monitor is known. The omnidirectional camera generates a video image using a fish-eye lens having 360 degrees of a horizontal field of view, and therefore this video image (referred to as an “omnidirectional image” below) has a circular shape or a donut shape and has characteristics that distortion becomes significant at a position closer to an outer periphery. Hence, a conventional display device can display not only display an omnidirectional image which allows an entire image capturing range to be checked but also display an image (referred to as a “distortion corrected image” below) obtained by correcting distortion of a clipping range of entirety or part of the omnidirectional image. Further, this switching of display is based on a user's instruction.
Meanwhile, a display device which displays a video image of an omnidirectional camera is used in, for example, the following scenes. In a business scene, a mobile terminal such as a mobile telephone is used as a display device to display a video image of an omnidirectional camera installed at a construction site, a facility or a store. Further, when an omnidirectional camera is used as a monitoring camera, the omnidirectional camera is installed at a monitoring target site such as a railway platform or a parking lot, a video image of the omnidirectional camera is displayed at a headquarter or a central control room and is monitored by security guards. Furthermore, when a worker installs an omnidirectional camera which is used as a monitoring camera, at a high place such as a telegraph pole, an installation work business operator adjusts an angle of view while checking a video image of the omnidirectional camera using a display device of a wearable display type such as a wrist watch type.
When the display device is realized by a personal computer which has a monitor, an operation inputting means such as a mouse and a keyboard is provided, so that a user can instruct switching display by operating this operation inputting means (see, for example, Patent Literature 1 and Patent Literature 2).